The present invention relates to reciprocating pumping apparatus, particularly to a pair of fluid driven reciprocating pumps, and more particularly to a pair of fluid driven reciprocating pumps having at least one power chamber controlling a signal valve assembly and each having an intake-exhaust valve.
Fluid driven reciprocating pump assemblies have been utilized for a variety of applications for pumping various types of fluids, such as fuel, liquid propellant, hydraulic fluid, and many other fluids in industrial processes, with the pump assemblies being powered by a source of compressed air, combustion products, etc. The reciprocating pump assemblies have included pumps of the free-piston and diaphragm types which function to divide the pump chambers into power and pumping sections. Alternatively, a free surface resulting from gravity has been used to separate liquid being pumped from a driving gas. Various valve arrangements have been developed, especially where the reciprocating pump assemblies operate in pairs or sets to control the driving fluid to the power sections thereof. These prior reciprocating pumping systems and control valve assemblies are exemplified by U.S. Pat. No. 4,021,156 issued May 3, 1977 to F. J. Fuchs, Jr. et al.; U.S. Pat. No. 4,854,832 issued Aug. 8, 1989 to R. K. Gardner et al.; U.S. Pat. No. 4,936,753 issued Jun. 26, 1990 to N. Kozumplik, Jr., et al.; U.S. Pat. No. 5,026,259 issued Jun. 25, 1991 to J. C. Whitehead et al.; and U.S. Pat. No. 5,222,873 issued Jun. 29, 1993 to J. C. Whitehead et al. More recently a less complex valving arrangement has been developed for pairs of fluid driven reciprocating pumps, either of the free piston or diaphragm types, which utilizes a signal valve attached to each pump assembly to control the intake-exhaust valve of the other pump assembly, and is described and claimed in copending U.S. application Ser. No. 08/081,695, filed Jun. 25, 1993, entitled "Valving For Controlling A Fluid-Driven Reciprocating Apparatus now U.S. Pat. No. 5,427,507 issued Jun. 27, 1995".
Fluid-driven reciprocating pumps of various types have been utilized extensively in industry, where compressed air and other pressurized fluids are widely used as power sources, rather than electricity. Water pumps which are used in a wet environment and driven by compressed air, for example, eliminate the electric shock hazard involved in using electric motors or electric-driven tools in wet environments. Also, pumps driven by compressed air simply stop when a downstream valve is shut, and power from the power source ceases to flow (no air flow is wasted). For electric pumps, current continues to flow when they stop for some reason other than shutdown, so that energy is wasted, and the electric motor may overheat. In an industrial plant setting, compressed air is available "on tap", and cost is often less when an air-driven mechanism is used instead of an electric-driven mechanism. Finally, pumps driven by a fluid such as compressed air can operate over a wide range in flow rate with a minimal change in operating pressure.
For the above reasons, air-driven pumps are widely used, and are produced by numerous companies. They typically have two air power chambers which are alternately pressurized to stroke the pump back and forth.
Many of the fluid driven pumps utilize a diaphragm in each chamber of the pump to separate the power and pumping chambers formed on the opposite side of the diaphragm. Diaphragm pumps historically have used a mechanical trip or a single-stage valve to control the reciprocating motion of the diaphragms. Mechanical trips need to be replaced often because the detent device and/or the springs lose their recoil tension.
Diaphragm pumps equipped with a single-stage valve are susceptible to stalling. When one of these pumps is operated at slow cycle speeds, or used to pump heavy material, the over-travel of the diaphragm is reduced and so is the duration of the shift signal. This condition may cause the valve to only partially shift or stop completely. Either of these conditions will keep the pump from running. In order to operate at any speed without spring-latch mechanisms or mechanical trips (which wear out) or complicated rotating parts, reciprocating machines driven by fluid require at least three moving parts to oscillate automatically, without stalling. This principle has been exploited by the more recent prior art. The standard class of mechanism in use is one in which the three parts are: 1) the main double-acting pump element (connected pistons or diaphragms), 2) an intake-exhaust valve which controls the flow into and out of both power chambers, and 3) a pilot valve. Near the end of a stroke, the main pump element contacts the pilot valve and moves it slightly, which pneumatically changes the state of the intake-exhaust valve. In these prior art mechanisms, the three moving parts are individually different so they are manufactured as distinct, separate items. In at least one commercially available pump, sold by The ARO Corp. as the ARO 1/2 inch Diaphragm Pump, and described in above-referenced U.S. Pat. No. 4,854,832, the pilot valve is off-center so that the entire assembly is unsymmetrical and therefore relatively complicated.
The above-referenced U.S. Pat. No. 4,854,832 uses a two-stage valve to control the reciprocating motion of the pump. A pilot valve supplies a pilot signal to the power valve throughout the entire stroke or cycle of the pump. The pilot valve of this pump system illustrated in FIGS. 1 and 2, is not connected to the diaphragm connecting rod or the diaphragms. The pilot valve is oriented between the air chambers so that mechanical force moves the pilot valve to signal position, which in turn shifts the power valve.
The air from the power valve of this prior pump system (see FIGS. 1 and 2) continues to shift the pilot valve and hold it in position, even after the mechanical force is removed. This action positions the pilot valve for the next cycle and maintains the pilot signal throughout the entire cycle of the pump. This non-symmetrical pilot valve design allows the pump to run a slow cycle speed and with heavy materials without the pump stalling and stopping the flow of production materials. However, this pilot valving arrangement is complicated and thus costly to manufacture, and the intake or exhaust fluid must flow through long narrow passageways within the valve assembly. In particular, the power valve of above-referenced U.S. Pat. No. 4,854,832 is a complicated four-way valve because it must provide for intake and exhaust of both power chambers. As a result, the intake and exhaust flow passageways are small and restrictive relative to the size of the power valve. One consequence of restrictive passageways for the exhaust flow is cooling and the formation of ice in the valve. Another difficulty with the complicated four-way power valve is that sliding surfaces and reciprocating seals are required, which results in wear. An additional drawback is that the operational states of both power chambers switch simultaneously, so that positive pressurization overlap of the two power chambers is impossible.
There is a need in the art for a simplified valving arrangement for fluid driven pumps. This need has been satisfied by the present invention which utilizes in one embodiment a fluid driven apparatus having back-toback power chambers. A signal valve assembly is connected to at least one of the pistons or diaphragms in the power chambers for controlling a pair of intake-exhaust valves, each connected to one of the power chambers and to a source of pressurized fluid. Thus, activation of one of the power chambers is controlled by the state of pressurization in the opposite chamber, with switch over accomplished by the signal valve at the end of each stroke. As a result of having a separate intake-exhaust valve for each power chamber, flow passageways are larger, valve seats can be used instead of reciprocating seals or sliding surfaces, positive pressurization overlap of the two power chambers becomes possible, and the pilot valve function can be incorporated into the rod which connects the two diaphragms.
Accordingly, the invention involves a pair of fluid driven pumps, similar to those disclosed in above-referenced U.S. Pat. No. 5,222,873, and utilizing an intake-exhaust/signal valve arrangement which operate on principles similar to that of above-referenced application Ser. No. 08/081,695 now U.S. Pat. No. 5,427,507. The present invention provides a fluid driven pump system which in one embodiment uses a back-to-back configuration to yield a bi-directional pump, and is simpler in construction than existing commercial systems. The present invention also eliminates a particular stall condition of the valves disclosed in above-referenced U.S. Pat. No. 5,222,873, for example.